---
title: "Addition and Condensation Polymers"
description: "Alkenes join up by opening their double bonds and losing nothing at all, while diacids with diols or diamines join by losing a small molecule each time. What was lost decides whether the chain can be "
canonical: https://lightmysky.com/learn/science/addition-and-condensation-polymers-mt_klu208vTI1
source: https://lightmysky.com/learn/science/addition-and-condensation-polymers-mt_klu208vTI1.md
retrieved: 2026-09-12
---

> **Agent view.** This is the Markdown twin of the page, for tools and assistants.
> When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md
> API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md
> Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt
> Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json
> Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`.

# Addition and Condensation Polymers

Alkenes join up by opening their double bonds and losing nothing at all, while diacids with diols or diamines join by losing a small molecule each time. What was lost decides whether the chain can be broken apart again.

Subject: Science · Area: Chemistry · Ages 17 to 18
Page: https://lightmysky.com/learn/science/addition-and-condensation-polymers-mt_klu208vTI1

## Ready when they can

- Draws the repeat unit of an addition polymer from its monomer, and the monomer back from the repeat unit
- Draws the repeat unit of a polyester and of a polyamide and names the small molecule lost
- Explains why condensation polymers can be hydrolysed while poly(alkenes) resist
- Links the forces between chains to the strength and melting behaviour of a named polymer

## Lesson: How plastic chains join and split again

Some plastics grow when alkene monomers open their double bonds and link up. Picture each double bond popping open so both end carbons grab a neighbour instead. Nothing leaves, so the chain just repeats the monomer formula.

**Example.** Take ethene joining into polythene, the stuff of carrier bags. You draw the repeat unit as CH2 CH2, and you can read it straight back to ethene. The monomer and the repeat hold the same atoms, only linked into a chain.

Other plastics join by squeezing out a small molecule at every link. You join a diacid to a diol to make a polyester, or to a diamine to make a polyamide, and each new link lets go of one water molecule. That ester or amide link can split with water again, so a polyester bottle can return to monomers while a polythene bag cannot.

**Tip.** You tell the two families apart by asking what was lost. If nothing left, the chain resists splitting with water. Strong attractions between chains, like hydrogen bonds in a polyamide, also lift strength and melting point above chains held by weak spreading forces.

**Recap.** Addition chains open double bonds and lose nothing, while condensation chains lose water at each link and can split back.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Carboxylic Acids, Esters and Hydrolysis](https://lightmysky.com/learn/science/carboxylic-acids-esters-and-hydrolysis-mt_QLxUs5cOH2)
- [Ceramics, Polymers & Composites](https://lightmysky.com/learn/science/ceramics-polymers-and-composites-mt_w83U-_noVR)

## Opens up

- [Mass Spectra and Infrared: Identifying an Unknown](https://lightmysky.com/learn/science/mass-spectra-and-infrared-identifying-an-unknown-mt_yotOEg9OTn)